Internal combustion engines such as diesel engines burn a mixture of air and fuel within the engine, generating mechanical power and a consequent flow of exhaust. Engine exhaust contains air pollutants, including unburned fuel, particulate matter such as soot, and harmful gases such as nitrous oxide or carbon monoxide. A modern engine must meet stringent emissions standards, which limit the amount and type of pollutants that the engine may discharge into the atmosphere.
Modern engines often use EGR systems to help reduce pollutants in the engine exhaust. An EGR system recirculates engine exhaust through the combustion chambers of an engine by mixing some of the exhaust with fresh air entering the combustion chambers. The exhaust-air mixture lowers the combustion temperature and helps to reduce the amount of undesirable pollutants produced during operation of the engine.
An exemplary EGR system is disclosed in U.S. Pat. No. 7,941,999 of Kasper et al. that issued on May 17, 2011 (“the '999 patent”). The '999 patent discloses an engine with a first cylinder bank and a second cylinder bank. Exhaust gases from a first cylinder group in the first cylinder bank are collected in a first section and supplied to a turbocharger. Exhaust gases from a second cylinder group in the first cylinder bank are collected in a second section and supplied to the charge air supply lines connected to the first and second cylinder banks. Exhaust gases from the second cylinder bank are supplied to a different turbocharger before being discharged to the atmosphere. The exemplary EGR system of the '999 patent also includes three control devices for setting the EGR rate. A first control device is located between the first and second sections. A second control device is located between the second section and the turbocharger. A third control device is located downstream from a cooler, which cools exhaust from the second section before supplying the exhaust to the charge air supply lines.
Although the system of the '999 patent may help lower engine emissions by re-circulating the exhaust through all cylinders of the engine, the system may still be less than optimal. Specifically, the number of control devices used by the system of the '999 patent may increase the cost and complexity of the engine. Additionally, the first and second control devices can be subjected to an extreme environment, leading to excessive wear and premature failure of these devices.
The engine system of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.